The present invention relates to turbine blade repair procedures and tooling. In particular, the present invention relates to a method for correcting the twist angle of a gas turbine engine blade.
A gas turbine engine commonly includes a fan, a compressor, a combustor and a turbine. During engine operation, working medium gases, for example air, are drawn into the engine by the fan and directed into and compressed in the compressor. The compressed air is channeled to the combustor where fuel is added to the air and the air/fuel mixture is ignited. The products of combustion are discharged to the turbine section, which extracts work from these products to produce useful thrust to power, for example, an aircraft in flight.
The compressor and turbine commonly include alternating stages of rotor blades and stator vanes. Compressor and turbine blades and vanes often include complex, contoured airfoil geometries designed to optimally interact with the working medium gas passing through the engine. One common feature of airfoil geometries is the blade twist angle. The twist angle is the angular displacement of the airfoil about a spanwise axis, such as the stacking line, from the root to the tip of the airfoil. During normal engine operation, the blade twist angle feature, which is a critical characteristic of gas turbine engine blades, decreases due to thermo-mechanical cycling and aerodynamic loading of the blades. The twist angle must be restored to the original manufactured condition during engine overhaul prior to returning the blade to service.
Turbine blade twist correction is commonly accomplished by clamping the blade root in a fixture and manually applying a load to the tip of the blade using, for example a two-handed wrench configured to clamp the blade tip. An operator twists the blade using the wrench, measures the blade twist angle, and repeats the twisting procedure until the correct twist angle is reached. Because the operator can only estimate how much force to apply each time, this approach often requires many iterations to achieve the desired twist angle. This results in a time-consuming, labor-intensive and costly process. This approach can also result in over-twist due to applying excessive force. Over-twisting is particularly problematic in blades prone to micro-cracking, such as blades made from a directionally solidified nickel alloy.
Therefore, improved tools and methods for correcting blade twist angle are needed.